1. Field of the Invention
The present invention relates to a gain adjustment apparatus, a gain adjustment method, and a tangible machine-readable medium thereof for a multiple input multiple output (MIMO) wireless communication system. More particularly, the present invention relates to a gain adjustment apparatus, a gain adjustment method, and a tangible machine-readable medium thereof that are capable of adjusting a relay station (RS) gain of an MIMO wireless communication system.
2. Descriptions of the Related Art
During the development of mobile communication systems from the third generation (3G) towards post-3G or even 4G, limited frequency spectrum resources have become a major impediment to develop wireless technologies. To enhance the data rate and utilize the frequency spectrum more efficiently, some technologies and approaches have been used to improve the efficiency of spectrum usage, for example, the optimized modulation scheme, the code division multiplexing system or the multiple input multiple output (MIMO) technology. Over recent years, MIMO technology has been widely adopted in the industry; such as the newly emerging Worldwide Interoperability for Microwave Access (WiMAX) standard and the new generation of Wireless LAN (WLAN) have both incorporated the MIMO technology therein.
MIMO refers to signals transmitted and received through multiple antennas synchronously. An MIMO wireless communication system is provided with a plurality of antennas both at the source end and the receiving end, so that data is transmitted through a plurality of signal transmission channels, thereby enhancing the data rate. More specifically, signals are divided into multiple streams at the source end, which are then transmitted synchronously through a plurality of antennas. Since the signals are transmitted through different signal transmission channels, they may have different arriving times at the receiving end. To prevent signals from failing to be combined due to different arriving times, the receiving end utilizes a plurality of antennas simultaneously to receive these signals, and then combines the separate signals by digital signal processing with recalculation to quickly and properly recover the original signal.
Because the signal has been divided before being transmitted, the throughput in a single signal transmission channel is decreased, and the transmission distance of the signal can therefore be enlarged. Accordingly, the MIMO technology can not only increase the transmission speed of signals without requiring any additional spectrum, but also can enlarge the signal transmission distance. Therefore, many wireless network apparatuses that emphasize signal transmission speed and transmission distance now have adopted MIMO technology. Undoubtedly, MIMO technology represents an important breakthrough in the wireless mobile communication field, and has also become a core technology for new generations of mobile communication systems.
On the other hand, although the WiMAX standard already provides a wider bandwidth, lower deployment costs, better quality of service (QoS) and expandability, there are still limitations of network coverage range and signal quality provided. Hence, the work group of IEEE 802.16 standards has further formulated the multi-hop relay standard (MMR-RS), which enlarges the network coverage range of the WiMAX standard by relay stations (RSs).
More specifically, for an MIMO wireless communication system with RSs, each of the RSs firstly receives signals from all source antennas and then processes them to increase the signal strength. Afterwards, the RS transmits the processed signals to the receiving antennas.
Depending on the different processing approaches, the signal processing schemes of the RSs are mainly categorized into the decode-and-forward framework and the amplify-and-forward framework. For RSs adopting the decode-and-forward framework, they perform regenerative processing on signals received from the source antennas, filter noises out of the signals through decoding, and then transmit the signals with noises having been filtered to the receiving antennas. On the other hand, for RSs adopting the amplify-and-forward framework, they perform non-regenerative processing on signals received from the source antennas, i.e., the RSs multiply the signals received from the source antennas with an amplifying gain directly without decoding and noise filtering, and then transmit the multiplied signals to the receiving antennas.
For RSs adopting the decode-and-forward framework, a lot of technologies for improving signal transmission quality have been proposed in the prior art, for example, space-time coding or beam-forming, which attempt to improve the signal transmission quality of RSs adopting the decode-and-forward framework. However, these technologies for improving the signal transmission quality of RSs adopting the decode-and-forward framework are inapplicable to RSs adopting the amplify-and-forward framework. Additionally, besides the problem of improving signal transmission quality, there is also no solution to solve the problem of improving the system capacity of MIMO wireless communication systems using RSs that adopt the amplify-and-forward framework.
In view of this, as the demands of system capacity of MIMO wireless communication systems are increased, it is highly desirable for wireless communication apparatus manufacturers to improve both the system capacity and signal transmission quality of MIMO wireless communication systems using RSs that adopt the amplify-and-forward framework.